1. Field of the Invention
The present invention relates to a technique of designing an optical network and particularly to a method for designing an optical network, an optical network, and a recording medium, adapted to efficiently accommodate paths of various client signals in an optical network of diversified network topology, such as ring, ring interconnection, and mesh.
2. Description of the Related Art
In optical networks represented by a WDM (Wavelength Division Multiplexing) network, paths of various client signals need to be accommodated.
Examples of the client signals include a SONET (ANSI T1.105 recommendation: Synchronous Optical Network Basic Description Including Multiplex Structure, Rates, and Formats) signal; an SDH (ITU-T recommendation G.803: Architecture of Transport Networks Based on The Synchronous Digital Hierarchy) signal; a Gb Ethernet® signal; a 10 Gb Ethernet® signal; and a Fiber Channel signal.
In recent years, an optical transmission/reception card for a WDM transmitting device having both branching/inserting function and transponder function for SONET signals and SDH signals (hereinafter referred to as SONET/SDH signals) has been developed, so that a SONET/SDH network can be established on a WDM network by using only a WDM transmitting device.
Conventionally, a SONET/SDH network has been established on a WDM network by individually preparing a WDM transmitting device for transmitting WDM signals and a SONET/SDH ADM (Add-Drop Multiplexer) device for transmitting SONET/SDH signals and by using the both devices. Furthermore, the networks thereof have been independently designed on respective WDM network and SONET/SDH network layers.
In the following description, the WDM network is used as a representative example of optical networks, and the SONET signal is used as a representative example of client signals. However, other types of optical networks and other types of client signals, such as SDH signals, can also be applied.
When a path of SONET signals is to be accommodated in the WDM network, the path in the WDM network through which the SONET signals pass needs to be in a form of ring topology considering protection against abnormal transmission (e.g., failure in a device, increased loss in lines, or disconnection).
In order to actually accommodate a path of the SONET signals in a ring topology, a wavelength ring of a predetermined band (e.g., a wavelength ring of 10 Gbps), which is a ring path for accommodating a bundle of client signal paths, needs to be assigned in the ring topology.
Then, respective client signal paths are accommodated in the assigned wavelength ring while considering the bandwidths of the respective signals. Thus, a plurality of wavelength rings may be assigned to one ring topology.
When a path of SONET signals is to be accommodated in the WDM network, network topology information is established by inputting information about a connection relationship among nodes in the WDM network to be designed. Then, all ring topologies that can exist on the WDM network are searched for on the basis of the network topology information and are held.
When a wavelength ring is to be assigned on the WDM network, a ring topology that is determined to be optimal by a designer is selected from among the searched and held ring topologies, and then a wavelength ring to accommodate, for example, ring paths of the SONET network is assigned on the selected ring topology. That is, accommodation design is performed on the basis of information about transmitting end nodes and receiving end nodes and signal bandwidths included in information of respective client signal paths so that the number of wavelength rings in the WDM network is the smallest and that the total amount of optical transmission/reception cards mounted on respective nodes required to accommodate the client signal paths is the smallest.
Also, optimization considering a transmission characteristic, e.g., the length of a wavelength ring to accommodate client signal paths is shortened as much as possible, is required. A ring topology satisfying the requirement needs to be selected from among many ring topologies through determination made by a designer.
A technique of automatically designing a network transmission path including ring protection is disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2000-232472).
The following problems may arise when paths of client signals such as SONET/SDH signals are to be accommodated in an optical network, such as the WDM network.
(1) It takes a lot of time to search for all ring topologies when the network topology is complicated.
(2) In a large scale of network where the number of all ring topologies is large, there exist a plurality of ring topologies capable of accommodating a SONET/SDH path. In that case, accommodation design needs to be performed by determining an optimal ring topology to accommodate the SONET/SDH path. However, the determination requires a lot of time, which inhibits efficient designing.
In a conventional method for counting all paths that can be obtained from topology information, very long time and enormous storage capacity are required as a network scale becomes larger, which degrades efficiency of designing. For example, in recent years, many fibers have been laid in urban areas in accordance with the demand for networks, and the topology has become very complicated accordingly. This causes enormous time to be required in designing networks.
With the increasing complexity of the topology and the increase in capacity of each ring network, a larger ring path is designed to accommodate more client signal paths. However, if the ring path is too large, signals cannot be transmitted in an optical form between devices, and thus a regenerator needs to be provided therebetween. This results in an increase in the cost accordingly.